In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium, to form characters and images. The ink-jet printing methods have been rapidly spread because of their various advantages such as easiness of full coloration, low costs, capability of using ordinary paper as the recording medium, non-contact with printed images and characters, etc.
Among such printing methods, in view of enhancing the weather resistance and water resistance of printed images and characters, an ink-jet printing method utilizing an ink containing a pigment as the colorant has now come to dominate. Further, there have been some proposals for improving the water-based inks for ink-jet printing.
For example, there have been disclosed a recording solution to which an emulsion obtained by conducting polymerization in the presence of a reactive surfactant is added to prevent clogging of nozzles with pigments (refer to JP 2002-294105A), and an ink composition that contains polymer particles containing a polyalkoxyalkylene derivative, etc., and a self-dispersible pigment to improve a high lighter-fastness and a rubbing resistance thereof (refer to JP 2001-329199A).
In addition, there have also been disclosed a recording solution containing a pigment and two or more kinds of fine resin particles having the same polarity when dispersed (refer to JP 2001-81366M, and a recording solution containing a self-dispersible pigment containing a hydrophilic group and two or more kinds of fine resin particles containing a hydrophilic group which is the same in kind as that contained in the pigment (refer to JP 2004-189879A).